1. Field of the Invention
The present invention relates to the improvement of a fuel supply apparatus to an internal combustion engine having a high-pressure pump and a high pressure regulator.
2. Description of the Related Art
An example of such a kind of conventional fuel supply apparatus to an internal combustion engine, in particular, a fuel supply apparatus which has been applied to an in-cylinder direct fuel injection type gasoline engine will be explained with reference to FIGS. 13 to 15. First, in FIG. 13, a reference numeral 1 designates a fuel tank in which gasoline is stored, 2; a low-pressure pump provided within the fuel tank 1, 3; a low-pressure regulator coupled to the low-pressure pump for adjusting the pressure of the fuel ejected from the low-pressure tank 2, 4; a high-pressure pump driven by the engine for ejecting the fuel supplied from the low-pressure pump 2 with a high pressure. The high-pressure pump 4 is secured to cylinder head or the like of the engine. A reference numeral 5 designates a delivery pipe coupled to an electromagnetic type injectors (not shown) for storing the high-pressure fuel supplied from the high-pressure pump 4 in a pressurized state. A reference numeral 6 designates a high-pressure regulator, for adjusting the fuel pressure within the delivery pipe 5 at a predetermined value, having one end coupled to the delivery pipe 5 and the other end returned to the fuel tank 1.
The detailed structure of the high-pressure regulator 6 will be explained with reference to FIGS. 14 and 15. In these figures, a reference numeral 60 designates a housing, 61; a passage formed in the housing and communicating with the delivery pipe 5, 62; a passage formed in the housing 60 and returned to the fuel tank 1 side, 63; a valve seat having a seat portion 63a serving as an abutment portion. A reference numeral 64 designates a valve, 64a; a seat portion capable of abutting against the seat portion 63a. A reference numeral 65 designates a spring pressing the valve to the valve seat 63 side, 66; a spring guide for guiding the spring threrealong, 67; an adjusting screw for adjusting the position of the spring guide 66, and 68; a spacer in which the adjusting screw is mounted so as to be screwed therein. The spacer 68 is secured to the housing 60. A reference numeral 69 designates a cylindrical sleeve attached between the valve seat 63 and the spacer 68 within the housing 60. The surfaces of the respective seat portions 63a and 64a are formed to have the Vickers hardness (Hv) of about Hv650.
According to such a fuel supply apparatus, the fuel pressurized to a some extent by the low-pressure pump 2 is further pressurized by the high-pressure pump 4 to a predetermined pressure value. In this case, the pressure of the fuel ejected from the low-pressure pump 2 is stabilized within a predetermined range by the low-pressure regulator 3, and further the pressure of the fuel ejected from the high-pressure pump 4 is stabilized within a predetermined range by the high-pressure regulator 6.
The fuel pressurized by the low-pressure pump 2 is further pressurized by the high-pressure pump 4, then supplied to the delivery pipe 5 and injected into the cylinders of the engine through injectors at predetermined timings.
The high-pressure regulator 6 operates in the following manner. That is, the valve 64 separates from the valve seat 63 against the biasing force of the spring 65 when the fuel pressure within the delivery pipe 5 exceeds a predetermined value. Thus, the fuel supplied from the delivery pipe 5 is returned to the fuel tank 1 through the clearance between the valve 64 and the valve seat 63 and the passage 62, and hence the fuel pressure within the delivery pipe 5 decreases. When the fuel pressure within the delivery pipe 5 decreases to the predetermined value, the valve 64 is pressed to the valve seat 63 side by the biasing force of the spring 65. Then, the valve 64 abuts against the valve seat 63 thereby to cut off the flow of the fuel to the return side. Thereafter, when the fuel pressure within the delivery pipe 5 increases and exceeds the predetermined value, the aforesaid operation is repeated again thereby to adjust the fuel pressure at the predetermined value.
According to the conventional high-pressure regulator 6, since the valve 64 abuts against the valve seat 63, the seat portions 63a and 64a serving as the abutment portions thereof are worn away.
In particular, in the case where the temperature of the fuel becomes high and the pressure of the fuel decreases at the time of passing through the seat portion 64a of the valve 64, the fuel boils and becomes gaseous. As a consequence, the valve 64 abuts against the seat portion 63a of the valve seat 63 in a substantially dehydrated state, so that the abutment portions thereof are worn away more easily.
Further, bubbles are generated in the fuel due to the fuel pressure reduction when the fuel passes through the seat portions 64a, 63a of the valve 64 and the valve seat 63, whereby the cavitation erosion is caused and so the surfaces of the seat portions 64a, 63a of the valve 64 and the valve seat 63 become uneven.
When the abrasion or the cavitation erosion are caused at the valve 64 and the valve seat 63 of the high-pressure regulator 6 in this manner, the sealing property between the valve 64 and the valve seat 63 is degraded, so that the high-pressure regulator 6 can not perform the pressure control operation normally. As a consequence, there arises a problem that the fuel pressure within the delivery pipe 5 decreases and hence the fuel can not be injected suitably from the injectors.
In particular, in the case of the abrasion, although the sealing property can be maintained so long as the abrasion portions of the valve 64 and the valve seat 63 do not slide to each other, the sealing property degrades when the abrasion portions thereof slides to each other.